1. Field of the Invention
The invention relates to a method for synthesis of hierarchically ordered materials at multiple length scales using polyalkylene oxide triblock copolymers.
2. Description of Related Art
Nature abounds in hierarchical structures that are formed through highly coupled and often concurrent synthesis and assembly process over both molecular and long-range length scales. [Aksay, et al., Science, Vol. 273, 892 (1996)]. The existence of these hierarchical structures, such as abalones and diatoms, has both biological and evolutionary significance. The special architecture of the natural structures make them simultaneously hard, strong, and tough. It has thus been a long-sought goal to mimic the natural process responsible for these exquisite architectures using biomimetic strategies to control the structural organization and thereby produce useful materials with similar architecture.
Several approaches are currently available for the preparation of ordered structures at different length scales. For example, organic molecular templates can be used to form zeolitic structures with ordering lengths less than 3 nm [Bu, P., et al., Science, Vol. 278, 2080 (1997)]. Mesoporous materials with ordering lengths of 3–30 nm can be obtained using surfactants or amphiphilic block copolymers as the structure-directing agents [C. T. Kresge, et al., Nature, Vol. 359, 710 (1992); D. Zhao, et al., Science, Vol. 279, 548 (1998); P. Yang, et al., Nature, Vol. 399, 48 (1998); A. Firouzi, et al., J. Am. Chem. Soc. Vol. 119, 9466 (1997); and S. H. Tolbert, et al., Science, Vol. 278, 264 (1997)].
Studies have shown the use of latex spheres affords macroporous materials with ordering lengths of 100 n–1 μm [O. D. Velev, et al., Nature, Vol. 389, 447 (1997); M. Antonietti, et al., Adv. Mater., Vol. 10, 154 (1998); B. T. Holland, et al., Science, Vol. 281, 538 (1998); and J. E. G. J. Wijnhoven, et al., Science, Vol. 281, 802 (1998)]. Soft lithography has also been shown to make high-quality patterns and structures with lateral dimensions of about 30 nm to 500 μm. [Y. Xia, et al., Angew. Chem. Int. Ed., Vol. 37, 550 (1998); E. Kim, et al., Adv. Mater. Vol. 8, 245 (1996); and C. Marzolin, et al., Adv. Mater. Vol. 10, 571 (1998)].
Previous studies have shown use of micromolding to form patterned mesoporous materials [H. Yang, et al., Adv. Mater., Vol. 9, 811 (1997); and M. Trau, et al., Nature, Vol. 390, 674(1997)]. These studies, however, used acidic aqueous conditions to carry out the cooperative self-assembly, which is disadvantageous because of the poor processibility of the aqueous solutions. [Q. Huo, et al., Nature, Vol. 368, 317 (1994)]. The results of these studies were that either non-continuous films were formed or an electric field was needed to guide the mesophase growth, which required a non-conducting substrate [H. Yang, et al., supra; and M. Trau, et al., (1997), supra]. Studies have also shown the use of latex spheres to make disordered macro- and mesoporous silica [M. Antonietti, et al., supra].
Although previous studies addressed the synthesis of disordered mesoporous silica and alumina, using nonionic surfactants as the structure-directing agents and alkoxides as the inorganic sources, under aqueous media, the studies did not address large-pore mesoporous materials with vastly different composition, and nanocrystalline frameworks [Sayari, A., Chem. Mater. Vol. 8,1840 (1996)].
Despite all of earlier efforts in nanostructuring materials, the fabrication of hierarchically ordered structures at multiple length scales has remained an experimental challenge. Such materials are important both for systematic fundamental study of structure-property relationships and for their technological promise in applications such as catalysis, selective separations, sensor arrays, waveguides, miniaturized electronic and magnetic devices, and photonic crystals with tunable band gaps [D. Zhao, et al., Adv. Mater. Vol. 10, 1380 (1998) and M. E. Gimon-Kinsel, et al., Stud. Surf. Sci. Cata., Vol. 117, 111 (1998)].
Many applications for macro- and mesoporous metal oxides require structural ordering at multiple length scales. Thus, there exists a need for hierarchically ordered materials and a method for forming the materials which overcome or minimize the above mentioned problems and which have enormous potential for a variety of immediate and future industrial applications. A need also exists for forming the hierarchically ordered materials using low-cost, non-toxic, and biodegradable polyalkylene oxide block copolymers.